1. Field of the Invention
The present invention relates to a resist composition suitable for lithography and the like, acting by radiation ray of high energy such as far ultraviolet ray (including excimer laser and the like), electron beam, X ray or radiation light and the like.
2. Description of Related Art
Recently, with progress in higher integration of integrated circuits, there occurs a requirement for formation of submicron patterns. Particularly, lithography using excimer laser from krypton fluoride or argon fluoride is paid to attention since it enables production of 64 M DRAM to 1 G DRAM. As the resist suitable for such an excimer laser lithography process, there is a tendency to adoption of a so-called chemical amplification type resist utilizing chemical amplification effect. In the case of the chemical amplification type resist, an acid generated from an acid generator at parts irradiated with radiation diffuses by the subsequent heat treatment (post exposure bake: hereinafter, abbreviated as PEB), and solubility of the irradiated parts in an alkali developer is changed in a reaction using this acid as a catalyst, and by this, positive patterns are provided.
A chemical amplification type positive resist is characterized by containing of a resin insoluble or poorly soluble itself in an alkali aqueous solution but becoming soluble in an alkali aqueous solution by the action of an acid, and an acid generator. However, such a resin is expensive.
When the protection ratio of a group unstable to an acid in a resin insoluble or poorly soluble itself in an alkali aqueous solution but becoming soluble in an alkali aqueous solution by the action of an acid is increased, resolution is improved in general. However, there are defects that unevenness due to standing wave of patterns increases, and pattern profile, particularly, line edge roughness deteriorates, and irregularity of process dimension increases.
If permeability of a photoresist is lowered to decrease unevenness due to standing wave of patterns and line edge roughness, resolution deteriorates.
An object of the present invention is to provide a chemical amplification type positive resist composition which decreases cost without lowering basic abilities such as sensitivity, resolution and the like, causes small unevenness by standing wave, and shows improved pattern profile, particularly, improved line edge roughness.
The present inventors have intensively studied to attain such an object, and resultantly found that cost can be reduced greatly without significantly deteriorating basic abilities of a resist, by mixing a specific novolak resin having a low content of components of lower molecular weights, in addition to a resin insoluble or poorly soluble itself in an alkali aqueous solution but becoming soluble in an alkali aqueous solution by the action of an acid, as the resin component of a chemical amplification type positive resist. The present invention was thus completed.
Namely, the present invention provides to a chemical amplification type positive resist composition comprising a novolak resin, a resin insoluble or poorly soluble itself in an alkali aqueous solution but becoming soluble in an alkali aqueous solution by the action of an acid, and an acid generator, wherein when the novolak resin is measured by gel permeation chromatography (GPC) using a 254 nm UV detector using polystyrene as a standard, the area ratio of components having molecular weights of 1000 or less is 25% or less based on the total pattern area excepting unreacted monomers.